FIG. 1 shows a portion of one known combustor system 10 of a turbine engine. The combustor 10 includes a combustor head-end 12, a transition duct 14, and a liner 16 extending therebetween. The term “combustor head-end” generally refers to the fuel injection/fuel-air premixing portion of the combustor 10. The liner 16 extends away from the combustor head-end 12 toward the transition duct 14. The liner 16 can connect between the combustor head-end 12 and the transition 14 in any of a number of known ways.
During engine operation, the liner 16 requires cooling because the high temperature of the combustion occurring inside of the liner 16 can threaten the structural integrity of the liner 16. One known scheme for air-cooling at least a portion of the liner 16 involves the use of a flow sleeve 18. The flow sleeve 18 surrounds a portion of the liner 16, so that an annular passage 20 is formed therebetween. Air 22 from the compressor section (not shown) can enter the combustor head-end 12 through the annular passage 20. As it travels through the passage 20, the air 22 is directed along the outer peripheral surface 24 of the liner 16 so as to cool the liner 16. In addition to cooling, the flow sleeve 18 can help to make the air flow through the combustor head-end 12 more uniform, resulting in better mixing with fuel, which in turn can reduce the formation of undesired emissions during combustion and can help to maintain more uniform temperature at the exit end of the liner 16.
The flow sleeve 18 is attached at one end 26 to one or more of the components in the head-end 12 of the combustor 10, such as the combustor casing 28. In one known system, the flow sleeve 18 is welded to one of the combustor head-end components. In another known system, the flow sleeve 18 is sandwiched or otherwise clamped between two or more components in the combustor head-end 12.
Experience has revealed a number of drawbacks with these attachment systems. For instance, they can introduce new fluid leak paths between the combustor head-end 12 and the flow sleeve 18. Fluid leakage can diminish engine efficiency and can have an adverse impact on engine emissions. Thus, complicated sealing systems must be devised. Moreover, the sandwiched flow sleeve attachment system usually involves high stack-up tolerances and interference issues because the flow sleeve 18 is directly engaging two or more components in the combustor head-end 12.
Further, the flow sleeve 18 and the components in the combustor head-end 12 to which the flow sleeve 18 is attached can undergo different rates of thermal expansion and contraction. As a result, high thermal stresses can be imposed on the area of attachment, which can lead to low cycle fatigue failures. In the case of a welded flow sleeve, such a failure can manifest as weld cracks.
Depending on the severity of the damage, the flow sleeve 18 may need to be replaced. Further, repair may be needed on other combustor components in the combustor section. In order to access any of these components for repair or replacement, the flow sleeve 18 must be removed. Removal of a flow sleeve that is welded or sandwiched between other head-end components is difficult, labor intensive and time consuming, and can result in extended outages. Likewise, upon completion of the repairs, the installation of the flow sleeve 18 and reassembly of the combustor head-end 12 is also a time consuming and difficult task. Detailed procedures must be developed to guide field technicians through the assembly and disassembly process. In light of the above, it will be appreciated that such attachment systems can significantly increase life cycle costs over the life of an engine.
In addition, some combustors may be located in an area in which a flow sleeve cannot be directly connected to the combustor head-end used because of interferences. One location in which interference concerns can arise is at or near an interface 30 between an upper combustor casing 32 and a lower combustor casing 34, a portion of which is shown in FIG. 2. The upper and lower casings 32, 34 can cooperate to enclose the combustor section 10 of the engine. The upper and lower casings 32, 34 abut along a plane that is substantially horizontal and is sometimes referred to as the horizontal joint 36. In one known engine design, a flow sleeve cannot be connected to the head-end 12 of a combustor system 10 located at or near the horizontal joint 36 because of an interference with large joint bolts 38 that connect the casing halves 32, 34. The joint bolts 38 protrude from the interface 30 and can be retained by a nut 40.
The welded and sandwiched flow sleeve attachment systems can also preclude or detract from the use of other desirable combustion components, such as certain pre-mix fuel rings. As a result, less efficient or less desirable systems may need to be employed to avoid potential interferences with the flow sleeve 18.
Thus, there is a need for a flow sleeve attachment system that can minimize such concerns.